The present invention relates to gas turbine engine casings, particularly gas turbine engine fan casings, more particularly to an improved blade containment assembly for use within or forming a part of the gas turbine engine casing.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor which is enclosed by a generally cylindrical, or frustoconical, fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
There is a remote possibility that with such engines that part, or all, of a f an blade, or a turbine blade, could become detached from the remainder of the fan or turbine. In the case of a fan blade becoming detached this may occur as the result of, for example, the turbofan gas turbine engine ingesting a bird or other foreign object.
The use of containment rings for turbofan gas turbine engine casings is well known. It is known to provide generally cylindrical, or frustoconical, relatively thick metallic containment rings. It is also known to provide generally cylindrical, or frustoconical, locally thickened, isogrid, metallic containment rings. Furthermore it is known to provide strong fibrous material wound around relatively thin metallic casings or around the above mentioned containment casings. In the event that a blade becomes detached it passes through the casing and is contained by the fibrous material.
However, in the event that a blade becomes detached, the blade strikes the metal casing and a significant load is imparted from the main impact region of the metal casing to a flanged interface with an intake casing.
It is normal practice to transfer the impact loads along the metal casing using a stepped increase in diameter of the metal casing, as shown in our published European patent application No. EP0965731A2. The stepped increase in diameter of the metal casing produces a local increase in stresses due to the bending moment at the stepped increase in diameter. The bending moments are counteracted by locally thickening the metal casing at the stepped increase in diameter of the metal casing. The locally thickened stepped increase in diameter adds weight to the metal casing, and the weight may be considerable if the metal casing is for a high bypass ratio turbofan gas turbine engine.
Accordingly the present invention seeks to provide a novel gas turbine engine casing which overcomes the above mentioned problems.
Accordingly the present invention provides a gas turbine engine rotor blade containment assembly comprising a generally cylindrical, or frustoconical, containment casing, the containment casing having an upstream portion, a blade containment portion and a transition portion, the upstream portion having a flange connecting the containment casing to an axially adjacent casing, the blade containment region being downstream of the upstream portion, the diameter of the upstream portion of the casing being greater than the diameter of blade containment portion and the thickness of the blade containment portion being greater than the thickness of the upstream portion, the transition portion connecting the blade containment portion and the upstream portion to transmit loads from the blade containment portion to the upstream flange, the transition portion having a smoothly curved increase in diameter between the blade containment portion and the upstream portion whereby the transition region is allowed to flex to reduce impact loads transmitted to the upstream flange.
Preferably the thickness of the transition portion being substantially the same as the thickness of the upstream portion of the containment casing.
The thickness of the transition portion may be between 75% and 125% of the thickness of the upstream portion of the containment casing.
The casing may have ribs and/or flanges. One or more continuous layers of a strong fibrous material may be wound around the casing.
The casing may comprise any suitable metal or metal alloy. Preferably the metal casing comprises a steel alloy, aluminium, an aluminium alloy, magnesium, a magnesium alloy, titanium, a titanium alloy, nickel or a nickel alloy.
An acoustic lining may be provided within the casing. The blade containment portion may have a radially inwardly and axially upstream extending flange, the flange being arranged at the upstream end of the blade containment portion.
The containment casing may be a fan containment casing, a compressor containment casing or a turbine containment casing.